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/*
* Alpha semaphore implementation.
*
* (C) Copyright 1996 Linus Torvalds
* (C) Copyright 1999, 2000 Richard Henderson
*/
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/init.h>
/*
* This is basically the PPC semaphore scheme ported to use
* the Alpha ll/sc sequences, so see the PPC code for
* credits.
*/
/*
* Atomically update sem->count.
* This does the equivalent of the following:
*
* old_count = sem->count;
* tmp = MAX(old_count, 0) + incr;
* sem->count = tmp;
* return old_count;
*/
static inline int __sem_update_count(struct semaphore *sem, int incr)
{
long old_count, tmp = 0;
__asm__ __volatile__(
"1: ldl_l %0,%2\n"
" cmovgt %0,%0,%1\n"
" addl %1,%3,%1\n"
" stl_c %1,%2\n"
" beq %1,2f\n"
" mb\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
: "Ir" (incr), "1" (tmp), "m" (sem->count));
return old_count;
}
/*
* Perform the "down" function. Return zero for semaphore acquired,
* return negative for signalled out of the function.
*
* If called from down, the return is ignored and the wait loop is
* not interruptible. This means that a task waiting on a semaphore
* using "down()" cannot be killed until someone does an "up()" on
* the semaphore.
*
* If called from down_interruptible, the return value gets checked
* upon return. If the return value is negative then the task continues
* with the negative value in the return register (it can be tested by
* the caller).
*
* Either form may be used in conjunction with "up()".
*/
void __sched
__down_failed(struct semaphore *sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down failed(%p)\n",
tsk->comm, task_pid_nr(tsk), sem);
#endif
tsk->state = TASK_UNINTERRUPTIBLE;
wmb();
add_wait_queue_exclusive(&sem->wait, &wait);
/*
* Try to get the semaphore. If the count is > 0, then we've
* got the semaphore; we decrement count and exit the loop.
* If the count is 0 or negative, we set it to -1, indicating
* that we are asleep, and then sleep.
*/
while (__sem_update_count(sem, -1) <= 0) {
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
remove_wait_queue(&sem->wait, &wait);
tsk->state = TASK_RUNNING;
/*
* If there are any more sleepers, wake one of them up so
* that it can either get the semaphore, or set count to -1
* indicating that there are still processes sleeping.
*/
wake_up(&sem->wait);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down acquired(%p)\n",
tsk->comm, task_pid_nr(tsk), sem);
#endif
}
int __sched
__down_failed_interruptible(struct semaphore *sem)
{
struct task_struct *tsk = current;
DECLARE_WAITQUEUE(wait, tsk);
long ret = 0;
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down failed(%p)\n",
tsk->comm, task_pid_nr(tsk), sem);
#endif
tsk->state = TASK_INTERRUPTIBLE;
wmb();
add_wait_queue_exclusive(&sem->wait, &wait);
while (__sem_update_count(sem, -1) <= 0) {
if (signal_pending(current)) {
/*
* A signal is pending - give up trying.
* Set sem->count to 0 if it is negative,
* since we are no longer sleeping.
*/
__sem_update_count(sem, 0);
ret = -EINTR;
break;
}
schedule();
set_task_state(tsk, TASK_INTERRUPTIBLE);
}
remove_wait_queue(&sem->wait, &wait);
tsk->state = TASK_RUNNING;
wake_up(&sem->wait);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down %s(%p)\n",
current->comm, task_pid_nr(current),
(ret < 0 ? "interrupted" : "acquired"), sem);
#endif
return ret;
}
void
__up_wakeup(struct semaphore *sem)
{
/*
* Note that we incremented count in up() before we came here,
* but that was ineffective since the result was <= 0, and
* any negative value of count is equivalent to 0.
* This ends up setting count to 1, unless count is now > 0
* (i.e. because some other cpu has called up() in the meantime),
* in which case we just increment count.
*/
__sem_update_count(sem, 1);
wake_up(&sem->wait);
}
void __sched
down(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down(%p) <count=%d> from %p\n",
current->comm, task_pid_nr(current), sem,
atomic_read(&sem->count), __builtin_return_address(0));
#endif
__down(sem);
}
int __sched
down_interruptible(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down(%p) <count=%d> from %p\n",
current->comm, task_pid_nr(current), sem,
atomic_read(&sem->count), __builtin_return_address(0));
#endif
return __down_interruptible(sem);
}
int
down_trylock(struct semaphore *sem)
{
int ret;
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
ret = __down_trylock(sem);
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): down_trylock %s from %p\n",
current->comm, task_pid_nr(current),
ret ? "failed" : "acquired",
__builtin_return_address(0));
#endif
return ret;
}
void
up(struct semaphore *sem)
{
#ifdef WAITQUEUE_DEBUG
CHECK_MAGIC(sem->__magic);
#endif
#ifdef CONFIG_DEBUG_SEMAPHORE
printk("%s(%d): up(%p) <count=%d> from %p\n",
current->comm, task_pid_nr(current), sem,
atomic_read(&sem->count), __builtin_return_address(0));
#endif
__up(sem);
}
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